This invention relates to devices for detecting motion or relative position between two parts and, more particularly, to devices for generating electrical signals in response to relative motion such as rotational speed sensors for the crankshaft of an internal combustion engine.
Heretofore, devices have been arranged to detect magnetic asymmetries between relatively moving parts. By magnetic asymmetries is meant periodic variations extending in the direction of relative motion of regions of high and low permeability. Such asymmetries usually consist of a sequence of teeth of ferromagnetic material with gaps between the teeth, which may be open or filled with a material of lower permeability. For example, the teeth of a gear rotationally fixed to a crankshaft provide magnetic asymmetries to indicate. the speed or rotational position of the crankshaft. With the inductive sensors customarily used for this purpose, voltage pulses are induced in a stationary coil during relative motion between the gear teeth and a stationary part, and the number of voltage pulses per unit time is a measure of the crankshaft speed.
When such devices are arranged to measure the crankshaft speed and the crank angle at a given time of an internal combustion engine of a motor vehicle, they must be capable of high resolution over a wide range of speeds since such engines may have a crankshaft speed varying from zero to about 10,000 rpm. Generally, the number of teeth on a gear used for this purpose may be about 120 and the voltage pulses are generated at a frequency between zero and about 20 kHz.
Conventional devices or sensors used for this purpose either lack the necessary ability to produce signals of constant amplitude over the entire engine speed or frequency range, or they fail to meet other basic requirements for use with automobile engines, such as mechanical ruggedness, adequate range of service temperatures, electrical and magnetic interference suppression, and suitability for mass production in terms of outlay and expense.
One significant disadvantage of sensors which rely on the inductive principle is the undesirable dependence of signal amplitude of the electrical signals on the frequency and/or speed or rotation. As a result, difficulties are encountered in maintaining tolerances, and elaborate signalprocessing electronics are necessary.
Conventional optoelectronic devices also lack the necessary signal fidelity and have been ruled out by signal fidelity and space requirements.
Sensors based on the Wiegand effect are technically advantageous, but they are too expensive for mass production for use in motor vehicle engines, for example.
Development of Hall sensors has not yet been completed. At present, the total outlay for the components required to generate signals, including signal processing and voltage supply, is too high.